FR: Rename feature 'certificates'

[ThomasMinor]

Since the feature certificates provides a means to add trusted certificate authorities to the CloudControl environment, the feature name should also reflect this purpose.

Please change the name og the feature to ca_certificates or tca.

Please add your opinions

[dploeger]

Hm. We need to think this through as it is a breaking change. They're still certificates, but certificates of CAs... I don't know.

[ThomasMinor]

I suggest to add the new name and deprecate the old one.
Then we could perform the breaking change release after some more or urgent breaking changes have to be made.